1. Field of the Invention
The invention relates to a method for casting a cast part from a metal melt and a suitable device for performing such a method. The metal melt processed according to the invention is in particular a light metal melt, preferably an aluminium- or an aluminium alloy-based melt.
2. Description of Related Art
The properties of a cast part are heavily influenced by the course of the solidification of the melt in the casting mould and the feeding necessary to compensate for shrinkage. Thus a particularly even distribution of properties results if the filling of the mould with melt is carried out in a continuous process avoiding high melt flows in the casting mould, and the solidification then starts with an even distribution on the opposite side of the casting mould from the feeder.
Particularly high-quality cast products can be produced by so-called rotation moulding. One embodiment of this moulding method that has been tried and tested in practice for the production of high-quality cast parts was proposed in DE 100 19 309 A1. According to this a melt container containing metal melt with its opening directed upwards is docked with a filling opening pointing downwards of a casting mould. Then the casting mould along with the melt container in a fixed connection with it is rotated through approximately 180°. In the course of the rotation the melt passes from the melt container to the casting mould. Once the final rotational position has been reached, the melt container is removed from the casting mould. The hot residual melt which is now located at the top in the feeder area can then remain effective through gravity and efficiently balance out the volume loss associated with the solidification of the melt.
Through the rotation of the casting mould with the melt container a complete filling of the casting mould with metal melt is achieved. Because in the course of the casting mould rotation the metal melt filling the casting mould is evenly subjected to gravity, the melt reliably reaches all areas of the mould cavity of the casting mould which reproduces the cast part to be cast. In addition, the structure of the cast part is optimised as a result of the directed solidification which is brought about by the alignment of the casting mould associated with the rotation.
Problems arise with the rotation moulding performed in the above way, however, when for cylindrical internal geometries particularly even solidification morphologies are required. As a result of the casting mould initially being filled against gravity and then rotated for cooling, a calmer filling of the mould and associated improved solidification can indeed be achieved. However, even before rotation, casting defects can arise which mostly take the form of bubbles or cold runs. These casting defects are due to the fact that the melt even before rotation of the casting mould cools to such an extent in the casting mould that uncontrolled solidification fronts (or ‘cold runs’) form or the melt contracts in the casting mould with the inclusion of bubbles.